Among thickeners, some of the most significant thickeners are water soluble polymers containing hydrophobic groups which are capable of forming intermolecular associations and adsorbing onto the surface of dispersed particles. This class of polymers is referred to as associative thickeners.
Associative thickeners or rheology modifiers provide necessary processing and performance characteristics to various compositions having diverse end uses. For example, thickeners are used in aqueous latex paints to provide a desired viscosity and to stabilize emulsions and pigment dispersions. Associative thickeners are used in waterborne coatings to improve the flow and leveling of coating films, improve film build and film formation, improve gloss, and reduce roller spatter. Thickeners are also used in the preparation of cosmetics and pigment pastes; textile manufacturing; and in many processes that involve the treatment of water including oil drilling and enhanced oil recovery operations.
Aqueous systems utilizing associative thickeners are often required to display an acceptable response to shear induced deformation encountered in the manufacture of the system, and also during application or use.
Associative thickeners are either naturally or synthetically derived compounds. Modified natural compounds which have been utilized in the art for many years include starch, cellulose, alginate, and protein. The natural thickeners generally include building blocks of polysaccharide units or amino acids, and grafting of selected moieties onto the backbone provides for modified versions utilized in different applications. The synthesized polymeric associative thickeners include acrylic-based polymers derived from acrylic acid or acrylate esters among others. The addition of hydrophobic moieties to the acrylic-based polymers has also been performed. Further synthetic associative thickeners include hydrophobically modified polyether-based polyurethanes and hydrophobically modified ethoxylated urethane resins which generally consists of polyethylene glycol units of varying length connected by urethane linkages with the polymer terminated with hydrophobic end groups. The prior art acrylic acid or acrylate associative thickeners typically exhibit inferior properties when compared to polyurethane associative thickeners, even at very high concentration.
U.S. Pat. Nos. 4,079,028, 4,180,491, and 4,425,485 disclosed the use of polyurethane having hydrophobic branching groups as thickeners. U.S. Pat. No. 4,514,552 discloses the use of ethoxylated hydrophobes in acrylic emulsions to make alkali soluble thickeners.